1. Field of the Invention
The present invention relates to a cylinder retraction system, a boom device and a crawler crane.
2. Description of Related Art
Japanese Laid Open Patent Publication No. 2006-56695 discloses a crawler crane equipped with a self mount/dismount device that allows a crawler to be self mounted/dismounted during an assembly/disassembly process. The self mount/dismount device performs a crawler self mount/dismount operation by using sheaves disposed at a lower boom and a hoisting device installed at a revolving upper superstructure.
However, the self mount/dismount device disclosed in the publication cited above requires a rope to be wound around the various sheaves at the lower boom and a heavy hook prior to the crawler mount/dismount operation and this preparatory work is both time-consuming and labor intensive.
As a way of addressing this issue, a cylinder-type self mount/dismount device, having a hydraulic cylinder swingably suspended in advance on the ventral surface side of the lower boom so as to allow the crawler to mount or dismount itself via the hydraulic cylinder, has been proposed. When the hydraulic cylinder is not in use in a crawler crane equipped with the cylinder-type self mount/dismount device, the hydraulic cylinder is held by connecting the front end of a rod, located at the lower end of the suspended hydraulic cylinder, with the lower boom via a belt sling, a rope sling or the like and keeping the rod in the hydraulic cylinder in the contracted state. When the hydraulic cylinder needs to be used, the rod is extended and the sling is taken off.